A chimeric or fusion protein for inducing an immune response to P. gingivalis, the protein comprising a first polypeptide linked to a second polypeptide, wherein: A) the first polypeptide comprises or consists of an amino acid sequence of the active site of an Arg- or Lys-gingipain of P. gingivalis, or a sequence that is at least 80% identical thereto; and B) the second polypeptide comprises or consists of an amino acid sequence of an adhesin domain of an Arg- or Lys-gingipain of P. gingivalis; and wherein the second polypeptide: a) comprises an amino acid sequence corresponding substantially to the full length of the DUF2436 domain of an Arg- or Lys-gingipain, or a sequence at least 80% identical thereto; and/or b) comprises one or more cysteine amino acid substitutions in the adhesin domain, compared to the naturally occurring Arg- or Lys-gingipain sequences in corresponding regions; and optionally comprises one or more amino acid motif substitutions in the adhesin domain for reducing multimerisation.

Antigen-binding molecules (ABMs) that bind to Porphyromonas gingivalis are described. The ABMs may be human or humanized ABMs. The ABMs find use in treating infections involving P. gingivalis, such as periodontal disease. Also provided are methods of treating or preventing a disorder or disease by administering the ABM.